The present invention is directed to bicycle derailleurs and, more particularly, to a bicycle derailleur with multiple mounting adjustments.
Typical bicycle rear derailleurs include a base member that mounts to the bicycle frame either directly or through an intermediate mounting member, a movable member coupled to the base member through a linkage mechanism so that the movable member moves laterally relative to the base member, and a chain guide mounted to the movable member. The chain guide typically includes a guide pulley and a tension pulley that engage the bicycle chain to guide the chain among a plurality of sprockets mounted to the rear wheel of the bicycle as the movable member moves relative to the base member.
Some derailleurs include an adjusting mechanism that allows the base member to be adjusted in a rotational direction relative to the bicycle frame. Such an adjustable derailleur is disclosed in U.S. Pat. No. 4,235,118. Other derailleurs, such as those disclosed in U.S. Pat. No. 4,690,663, include a base member that is rotatably mounted to the bicycle frame through a pivot shaft, wherein a torsion spring is mounted between the base member and a stopper plate that is rotatably mounted to the pivot shaft. The pivot shaft may be mounted either directly to the bicycle frame or indirectly through an intermediate member. An adjusting screw screws into a threaded opening in the stopper plate and contacts an abutment on the bicycle frame or on the intermediate member. Rotating the adjusting screw adjusts a twist angle of the torsion spring to adjust a biasing force applied between the stopper plate and the base member.
For optimum shifting, the distance between the guide pulley and the various sprockets, called “chain gap,” should be made as small as possible. The derailleur disclosed in U.S. Pat. No. 4,690,663 provides a spring balancing mechanism to accomplish this goal. However, such a spring balancing mechanism cannot accommodate some of the more extreme frame configurations in some modern bicycles. For example, when the base member is coupled to the frame through an intermediate member, the intermediate member may be so large that the adjustment mechanism disclosed in the patent cannot fully accommodate the significantly increased chain gap caused by the intermediate member.